American travelers are increasingly dissatisfied with the nation’s airlines, but they seem pretty happy with the country’s car rental companies.

For the first nine months of this year, the U.S. Bureau of Transportation Statistics got 12,145 consumer complaints about airline services, up 33.5 percent from a year earlier. Based on complaints filed in September alone, the biggest sources of aggravation for fliers were flight delays, cancellations, problems with baggage, ticketing and reservations and, of course, customer service.

Meanwhile, customer satisfaction with rental car companies has increased for the third consecutive year, according to a study released last week by J.D. Power & Associates. In fact, the satisfaction level — reaching 769 on a 1,000-point scale — is the highest in seven years.

The greatest improvement in the satisfaction rating came from the shuttle van or bus service that car rental companies use to transport customers and the daily rates and fees, according to the study.

Another big factor in higher satisfaction: a warm smile. The study found that car rental customers give an average rating of 795 when they are greeted at the counter with a smile; those who don’t get a smile give an average rating of 647.